Performance-management systems such as WebSphere XD (commercially available from International Business Machines, Armonk, N.Y.) operate by distributing workload across a collection of servers in order to meet (or exceed) performance goals set by administrators. Heretofore, the cost of the electrical power used to run the servers has not been taken into account in distributing workload across servers.
Rather, prior methods of combining power- and performance-considerations have focused on modifying servers' operational characteristics. Dynamic voltage scaling permits a reduction of power usage by lowering processor voltage at times of low CPU utilization. Dynamic frequency scaling reduces clock frequency, permitting the CPU to consume less power. Server consolidation involves consolidating workloads onto a minimal number of servers then powering off spare server machines. The decision whether to power a server on or off is made based on, for example, the operating frequency of currently running servers.
All of these known methods, however, presuppose a certain level of control over the servers' power usage. This control is not universally available, however; nor is it without cost even where available (e.g., it generally requires the use of special-purpose software). For this reason, it is desirable to have a system in which power-usage may be reduced without the need for modifying the servers themselves.